Tungsten base contact



Patented Mar. 18, 1941 UNITED STATES PAlENT OFFICE,

TUNGSTEN BASE CONTACT wa're No Drawing. Application February 24, 1939,Serial No. 258,182. Renewed June 14, 1940 6 Claims.

This invention relates to improvements in tungsten base contacts.

An object is to provide a new and superior alloy for electricalcontacting purposes.

It is another object of the invention to provide a tungsten base alloycontaining compounds of high melting points.

A further object of the invention is to provide a contact material whichpossesses, in addition to an inherent low average contact resistance,the ability to resist material transfer under heavy electrical loads.

It is a further object of the invention to produce an electricalmake-and-break contact which has less tendency for arcing and pittingduring operation, than the materials of the prior art.

Other objects of the invention will be apparent.

from the following description, taken in connection with the appendedclaims.

The present invention comprises the combination 'of elements, methods ofmanufacture and the product thereof, brought out and exemplified in thedisclosure hereinafter set forth, the scope of the invention beingindicated in the appended claims.

While a preferredembodiment of the invention is described herein, it iscontemplated that considerable variation may be made inthe method ofprocedure and combination of elements, without departing from the spiritof the invention.

According to the present invention, an improved alloy is contemplated,having the following ingredients, present in substantially the ranges ofproportions given below:

Metal taken fromthe group consisting of-- Per cent Tungsten, molybdenumand rhenium 90 to 99.8 Boride of boride forming elements of the 4th and5th group (particularly titanium, zirconium and hafnium and vanadium,columbium and tantalum) .1 to

We have found that special combinations within the composition rangesgiven above produce highly desirable alloys for, contact applications.The following combinations are given by way of ex- .ample only:

' Per cent Tungsten 97.5 Columbium boride 2.5

Tungsten 95.

Hafnium boride 5 Tungsten-.. 80

Molybdenum Tantalum boride 5 Tungsten 98 Zirconium boride 2 Tungsten96.5

Titanium boride 3.5

A useful group of compositions is the one in which tungsten makes up 60to 99.8% of the alloy, the boride of the 4th or 5th group metalamounting to .l to 10% of the composition and the balance of the alloybeing made up essentially of molybdenum or rhenium or both.

It has been found that in electrical systems wherein material transfersor build-up is the main factor to be considered, that the application ofsuch combinations as mentioned above in either positive or negativepositions, depending upon circuit characteristics, will produceoperating characteristics far more satisfactory than was possible withprior art materials. Specifically, combinations based upon the presentdisclosure operated 100% satisfactory, for periods in excess of 500hours continuous operation, whereas combinations of prior art producedfailures prior to 250 hours under the same condition. The operation wassatisfactory. both from the standpoint of build-up and oxidationcharacteristics.

While the majority of tests to date have been conducted on directcurrent, at relatively low voltages, indications are that thecombinations covered by the present disclosure will operatesatisfactorily on both A. C. and D. C. circuits,

at contact burdens of much greater magnitude.

It has also been found possible with these new contact alloycombinations to change the circuit characteristics materially, such asthe capacity or inductance in arc quenching circuits, and.

improve the performance still further.

It has been definitely established bya series of tests, that erosion onelectric make-and-break contacts is'initially established in the grainboundary material. This condition continues and is especiallyundesirable where the quantity of grain boundary material is relativelylarge and susceptible to contamination by oxides of the contact formingelements. In view of the grain size contrast encountered in thematerial, it has been noted experimentally that entire grain particlescan be electrically transferred from one operating member to the other,forming a nucleus for additional metal transfer.

The presence of borides materially assists in reducing the grainboundary erosion through the elimination of oxides and the formation inthe grain boundary material and grains of uniformly dispersed borides.This greatly reduces the tendency for electrical displacement ofmetallic particles in the active operating area.

In many cases a contact of the composition herein disclosed may be usedin co-operation with a mating contact of pure tungsten and theadvantages of the improved composition be obtained thereby.

In carrying out the invention, the new materials are usually formed fromfinely divided particles of the various elements and the borides to beincorporated into the ultimate composition, the said composition beingsubjected to a high pressure after properly mixing, to form an ingot orspecial shapes may then be sintered and used either in the as sinteredcondition or as sintered and forged, or after forging, and swaging, theymay be rolled or drawn out to a convenient shape, from which the contactparts can be manufactured.

It is understood that the metallic ingredients of the composition can bepresent originally in the form of oxides or other suitable chemicalcompounds and can be reduced together to the metallic state. Sinceye'ryhigh sintering temperatures are necessary, the-different ingredientswill difiuse in a very short'z'time into each other, producingcombinations having improved physical, chemical and electricalproperties.

What is claimed is:

1. An electric contacting element composed of metal or metals taken fromthe group of tungsten, molybdenum and rhenium, in percentages rangingfrom 90 to 99.8% and borides of the boride forming metals of the fourthand fifth group of the periodic system in percentages ranging from .1 to10%. 2. An electrical contacting element composed of 90 to 99.8%tungsten and .1 to 10% of material selected from the group consisting ofvanadium, columbium and tantalum boride.

3. An electrical contacting element composed of 90 to 99.8% tungsten,and .1 to 10% of the boride of a metal taken from the group consistingof titanium, zirconium and hafnium.

4. An electrical contacting element composed of metal taken from thegroup consisting of molybdenum, tungsten and rhenium in percent- I agesranging from 90 to 99.8%, where the tungsten content is at least 60% orhigher, and borides of the boride forming metals of the fourth group ofthe periodic system, in percentages ranging from .1 to 10%.

5. An electrical contacting element composed of metal taken from thegroup consisting of molybdenum, tungsten and rhenium, in percent agesranging from 90 to 99.8%, where the tungsten content is at least 60% orhigher, and borides of the boride forming metals of the fifth group ofthe periodic syste in percentages ranging from .1 to 10%.

6. The combination of two electrical contacting elements working againsteach other, one of which comprises a material of claim 1 and the otherone being substantially pure tungsten.

FRANZ R. HENSEL. KENNETH L. EMMERT.

